Immersion heaters with heating elements in the form of printed circuit tracks

ABSTRACT

An immersion heater has a support plate on which there is provided an electrical heating element in the form of a printed circuit conductive track. The element is provided with a portion which allows it to be clamped in direct relation to a control unit in order to provide direct electrical, thermal, and mechanical connection to that unit. This allows the control unit to operate in the same manner as a control unit connected to a conventional immersion heater. A water heating vessel using the immersion heater mounted to a control unit through an aperture in the base of the vessel is also disclosed.

FIELD OF THE INVENTION

This invention relates to electric immersion heaters.

BACKGROUND AND SUMMARY OF THE INVENTION

Electric immersion heaters are very widely used in water heatingelectric appliances such as kettles, hot water jugs, washing machines,dish washers, urns etc. The standard form of immersion heater comprisesan elongate metal sheathed element which is formed into a tortuousconfiguration to provide the required length of element within the sizeconstraints of the water heating vessel. It is traditional that theelement terminates in so-called cold leads by means of which electricconnections are made to the heater. There is also generally provided anintermediate "hot return" portion which in use is in thermal contactwith a thermally sensitive actuator of a control device whichincorporates a switch for disabling the heater in the event of itoverheating in consequence of there being insufficient water in thevessel to cover the element.

Such immersion heaters are used as standard in most electric kettles andhot water jugs. They are traditionally located in the lower part of sucha vessel so that a minimum amount of water can be boiled. Since animmersion heater is substantially surrounded by water, heat generatedfrom all sides of the heating element is dissipated which renders animmersion heater more efficient than heaters which are mountedexternally of the water containing vessel and which heat the water via avessel wall. This latter form of heater is less efficient in that heatdissipated from the side of the heating element remote from the vesselwall is essentially wasted. Such heaters are generally run at a highertemperature than immersion heaters and therefore more prone to failure.

Known immersion heaters do have certain drawbacks. In particular, theyare, to an extent, aesthetically unpleasing. This is particularly sowhen they become covered in scale as is inevitable in the longer term.The shape of known heating elements makes them difficult to clean, andit is also difficult to clean the base of the vessel even though thisremains visible through the heater. Whilst in the UK and other countriesusers of electric kettles and hot water jugs have to a degree acceptedthe unpleasing appearance of the lower region of the vessel interior, insome countries there is a strong reluctance for this reason to useimmersion heaters and it is still more common to find the less efficientexternally mounted heaters discussed above.

Viewed from one aspect the invention provides an electric immersionheater comprising a support plate which is provided on at least one sidethereof with a heating element in the form of a printed circuitconductive track and incorporating a clamping part which is adapted tobe clamped in relation to a control device of the type having athermally sensitive actuator which cooperates with a switch diasablingthe heater in the event of it overheating, the clamping part beingeffective to provide heating for the thermally responsive actuator ofthe control device.

The support plate should be heat conducting and is preferably formed ofmetal e.g. stainless steel. It is particularly advantageous, althoughpossibly not essential in all applications, that the heating element isprovided on the side of the plate which faces downwardly in normal useof the heater.

An immersion heater in accordance with the invention has a number ofadvantages compared with known immersion heaters. If mountedhorizontally adjacent the base of an electric kettle or hot water jug,for example, the user sees the flat upper surface of the support platewhich is aesthetically more appealing and easier to clean than knownforms of heating element. If the printed circuit heating element isprovided only on the underside of the plate, it is not visible to theuser and is protected from damage. A heater in accordance with theinvention is more compact than a traditional immersion heater ofcomparable power. As with known immersion heaters, heat dissipated fromboth sides of the element is utilised for heating liquid.

Printed circuit heaters are known in other contexts and the form of theprinted circuit conductive track which forms the heating element mayvary. In one embodiment, the heater is formed by depositing one or morethin glass layers on the surface of a stainless steel support plate,followed by the printed circuit conductive track formed e.g. ofpalladium silver. Finally, a further layer or layers of glass aredeposited over the printed circuit track so that it is insulated fromthe water. Three layers of glass above and below the track are preferredto ensure water tightness. Such an arrangement can be formed from knownprinted circuit technology. Stainless steel is preferred because it doesnot significantly oxidise at the high temperatures--e.g. 950° C. --atwhich the depositing process is performed. Furthermore, it has a hightemperature coefficient of expansion, and therefore on cooling willcontract more than the glass layers deposited thereon. The glass istherefore placed in compression rather than tension whereby there is alesser tendency for it to crack.

It is preferred that the heating element follows a tortuous path and itis also preferred that the heating element terminates in respectivecontact portions adapted to make electrical connection with anelectrical control device for the heater in use. The glass coating isinterrupted in the regions of the contact portions so that electricalconnection can be made thereto. In a preferred form, the contactportions are provided with a lower resistance coating of e.g. silver sothat there is no substantial heating in the region where electricalconnection is made thereto. Such portions are therefore analogous to thecold leads of a traditional immersion heater.

The clamping part of the heating element is analogous to the so-called"head" part or mounting plate of known immersion heater assemblies. Insuch an arrangement, a heater mounted within a vessel may convenientlybe clamped in relation to a control device mounted externally to thevessel via an opening in the vessel wall.

Such a combination of heating element and control device is consideredto contain inventive matter and therefore, viewed from a second aspect,the invention provides an electric immersion heater and control devicearrangement comprising an electric immersion heater having a heatingelement in the form of a printed circuit conductive track, and a controldevice having a thermally sensitive actuator which co-operates with aswitch for disabling the heater in the event of it overheating, whereinthe control device is arranged in relation to the heater such that thethermally sensitive actuator is in thermal contact with part of theheating element of the immersion heaters.

The invention also extends to a water heating apparatus incorporatingsuch a combination and therefore, viewed from a third aspect there isprovided an electric water heating apparatus comprising a vessel and anarrangement as previously described, wherein the immersion heater isprovided within the vessel and the control device is mounted externallyto the vessel, part of the heating elements being in thermalcommunication with the control device via an opening in the vessel wall.

The clamping part of the heater may be provided with mounting studs orbolts which extend through the vessel wall opening to cooperate with thecontrol device. This is the same as a traditional immersion heatermounting arrangement. A ring shaped seal surrounds the opening in thevessel wall, the heater being clamped against such seal such that thecontact portions of the printed circuit element discussed above arelocated in the "dry" region circumscribed by the seal.

In known immersion heaters it is necessary for the cold leads to extendthrough the heater head from the wet side to the dry side. This adds tothe cost and complexity of the assembly. In accordance with theinvention, however, the heating element is substantially flat and maytherefore pass under the seal without disturbing it. Thus, in accordancewith the invention the printed circuit heating element need not extendthrough the clamping part of the heater but rather passes between thesupport plate and the seal.

It is preferred that an immersion heater in accordance with theinvention is configured for use with a standard form of control deviceused in relation to known immersion heaters. In this regard, the contactportions described above are preferably located in relation to theclamping part of the heater in a position similar to the cold leads of atraditional immersion heater. Known control devices are provided withspring contact members configured to make electrical connection with thecold leads when the control device is mounted to the immersion heaterhead. Such control devices could be modified for use with a heater inaccordance with the invention by providing conductive rods to cooperatebetween the planar contact portions of the heater and the spring contactmembers of the control device.

As described above, in known immersion heaters there is generally a hotreturn part of the element which is brazed to the wet side of the heaterhead and is in thermal contact with a thermally sensitive actuatingmeans of the control device located on the dry side, the actuating meansopening a switch and disabling the heater in the event of the elementoverheating. In accordance with the invention, there is no need for ahot return part of the heating element as such. Rather, since theheating element itself extends to the dry side of the clamping part ofthe heater where it terminates in contact portions as described above, aregion or regions of the element adjacent the contact portions is/areeffective to provide the heating for the thermally responsive actuatingmeans of the control device.

In known printed circuit technology it is most convenient to deposit theconductive track at a constant thickness. The width of the track mayhowever be readily varied to vary its resistance. Thus, at any regionalong the track's length the degree of heating can be reduced byincreasing the width of the track and increased by reducing its width.In a preferred embodiment of the invention the width of the track isslightly increased in the region where it passes beneath the seal inuse. This is to avoid excess heating of the seal which might damage it.

Safety standards now require for many forms of appliance that there be abackup heater disabling mechanism which is operable in the event thatthe switch provided in the control device as the primary protectorshould fail. The backup protector in known controls is generally a oneshot device such as a thermal fuse. In accordance with a preferredembodiment of the invention, the printed circuit heating element isprovided with one or more higher resistance portions adaptedpreferentially to rupture and therefore disable the heater in the eventof a serious overheat condition consequent upon failure of a primaryprotector in the control device. As discussed, the region of higherresistance may conveniently be formed by a region of reduced trackwidth. It is preferred that the higher resistance portion or portionsis/are provided in the dry region of the heater i.e. the region which inuse will be within the seal associated with the vessel wall opening. Thereason for this is that if, in extremism, rupturing of the elementcauses the insulating layer provided thereon to crack then there isstill no risk of live parts being exposed to water.

In most known immersion heater configurations the head part of theheater is vertically disposed in use for clamping in relation to a sidewall opening of the vessel. Thus, in one form of the invention theheater includes a clamping part extending upwardly in use at about rightangles to the main heating part of the heater. The end portions of theheating element extend from beneath the support plate around to the dryside of the clamping part where they terminate in contact portions asdescribed above. The support plate is preferably a unitary member bentinto a flattened L-shape when viewed in side elevation.

The embodiment described above requires that the printed circuit trackextends around the convex side of the sharp bend in the support plate.This can complicate the printed circuit forming process.

Accordingly, in a further embodiment the support plate is entirelyplanar and the clamping part is formed approximately centrally in theunderside thereof with the heating element substantially surrounding theclamping part in a tortuous and preferably curved path. Such anarrangement is suitable for use in a configuration where the heater isclamped to a control device located beneath the base of a vessel via anopening in the base wall.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings, wherein:

FIG. 1 is an underneath plan view of a first embodiment of immersionheater in accordance with the invention;

FIG. 2 is a side elevation;

FIG. 3 is an end elevation showing the dry side of the heater clampingpart;

FIG. 4 is a top plan view;

FIG. 5 is a section along line V--V in FIG. 4; and

FIG. 6 is an underneath plan view of a second embodiment of heater inaccordance with the invention.

FIG. 7 is a partially sectional view of an electric water heating jugincorporating an immersion heater in accordance with the secondembodiment of the invention.

FIG. 8 is an enlarged view of a portion of FIG. 7, showing a controlunit in section.

FIG. 9 is a plan view of an immersion heater according to a thirdembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIGS. 1 to 5, the immersion heater comprises astainless steel support plate 1 which is bent into a flattened L-shapeconfiguration as shown in FIG. 2. The support plate therefore comprisesa main heating portion 2 and a clamping part 3 which in use may beclamped in relation to a standard form of thermally-sensitive controlused with a traditional immersion heater. Examples of such controls aredescribed, for example, in GB-B-2181598 and WO 92/05675. Accordingly,the clamping part 3 is provided with studs 4 which in use extend throughan aperture in the wall of an associated heating vessel (not shown) forengagement with the control device. As is traditional, a resilient ringshaped seal (not shown) is associated with the opening such that thecentral region of the heater clamping part shown in FIG. 3 whichconfronts the control and which is circumscribed by the seal is keptdry.

As shown in FIG. 1 the underside of the support plate is provided with aheating element in the form of a printed circuit track 5. The track isdeposited between insulating layers of e.g. glass. The end portions ofthe track extend around the convex side of the bend in the support plateso as to terminate at contact portions 6 as shown in FIG. 3. The glassis removed above the contact portions 6. These contact portions arepreferably provided with a coating of low electrical resistance such assilver. This means that there is no substantial heating in the contactportions themselves.

Electrical connection with an associated control device may in use bemade between the contact regions 6 and spring connectors in the controldevice by means of connection rods 7. These rods are separate memberswhich are mounted by being sandwiched between the respective contactsurfaces 6 and the control device connectors when the control device ismounted to the clamping part 3 of the heater.

A dimple 8 is formed in the clamping part 3 of the heater adjacentspaced end parts 9a of the heating element which extend from the bend inthe support plate up to the contact portions 6. Those skilled in the artwill recognise such a dimple 8 as a mounting location for a bimetallicactuating means of a standard control device. Thus, in use the actuatingmeans is in good thermal contact with the parts 9a of the element and isadapted to open a switch and disable the heater in the event of itoverheating in consequence of not being covered by sufficient water.

It will be appreciated that, in accordance with the invention, there isno need for a traditional hot return part and, furthermore, cold leadsextending through the element head part are also not required. This isin consequence of the printed circuit element track being able to passbetween the seal and the mounting plate without disturbing the efficacyof the seal.

As shown in FIG. 3 the end parts 9a of the heating element are ofreduced width. As described above, these regions are intended topreferentially rupture in the event of a serious overheat conditionconsequent upon failure of the bimetallic actuating means or switchmeans in the control device. Since the parts 9a are within the seal theyare dry. This provides an extra safety feature in that, should theinsulating layer rupture, there is still no risk of live parts beingexposed to water. In the first embodiment with its vertical clampingpart 3, the parts 9a should be level with or preferably below thebimetallic actuating means of the control. Otherwise, there would be adanger of the parts 9a rupturing in advance of an operable bimetallicactuating means disabling the heater if a container is filled with waterto a level above the actuating means but below the parts 9a.

There are also regions 9b of increased width of the conductive track atthe point where it passes beneath the seal. This provides a region ofreduced heating which may be required to avoid damage to the seal.

In the illustrated embodiment, the main track is 5 mm wide, the parts 9aare 41/2 mm and the parts 9b are 6 mm.

A second embodiment of the invention is shown in FIG. 6. In thisembodiment, the support plate 1 is completely flat. The clamping part 3is the central region of the plate. The dry side of the clamping part 3is in use contained within the broken line 10 which corresponds to theposition of the seal in use. The main portion of the heating element 5surrounds the clamping part. It will be appreciated that this embodimentis intended for use in a vessel wherein the control device for theimmersion heater is mounted beneath a base wall of the vessel and theheater is clamped to the control device via an opening in such basewall. Accordingly, mounting studs or bolts 4 project downwardly from theheater through the base wall opening. Otherwise, the features of theheater described above in relation to the first embodiment are similarlyprovided in the second embodiment and like reference numerals are used.The circular configuration of heater 5 enables a maximum length ofheating element track to be provided within a minimum diameter ofsupport plate. A square support plate is illustrated but in practicethis would preferably be circular also.

FIGS. 7 and 8 illustrate the heater 1' of the second embodiment mountedthrough an opening in the base wall 10 of an electric water heating jug11 to a control unit 12. The jug is of the cordless type and is providedwith electrical contacts 13 (which form part of the control unit 12) ina recessed portion of its lower surface. These provide electricalconnection to a base unit (not shown).

The cut-away portion at the bottom of the jug may be provided with anoperating lever, or alternatively the jug base may be provided withcontrol apparatus as described in GB 2222025. The cut-way upper portionof the jug is of conventional design, and may also be as illustrated inGB 2222025. The jug forms a water receiving portion 14. This is boundedby side wall 15 and base wall 10. The base wall is formed in twoportions, one of which 10a is level with the bottom of the vessel andthe other part 10b is raised above the base of the vessel in order toprovide a dry chamber in which the control unit 12 is located.

The control unit illustrated is similar to that commercially availableas the Strix R32 control and described in detail in GB 2181598. The unitis clamped to heating element 1' as described previously via an openingin the base wall portion 10b. In the illustrated apparatus, bolts 16pass through holes in the heating element 1' and through the mountingholes in the control unit 12 to nuts located in recesses on the far sideof the control unit. Alternatively, the element may be provided withstuds such as those found on conventional heating elements. A resilientring shaped seal 17 is provided between the heating element 1' and thebase wall 10 in order to provide a water tight seal.

The control unit 12 is provided with a steam operated bi-metal 18 whichswitches off the kettle when water within it boils. In order for this tooperate, a steam channel 19 is provided outside one of the walls of thejug. Its lower end is located adjacent to the steam operated bi-metaland at its upper end, near the top of the jug, an aperture is providedwhich communicates with the water receiving portion 14. This allowssteam produced by water boiling within the vessel to operate the controlunit in the conventional manner.

Beneath the control unit a cover 20 is provided which in combinationwith a lower part of the outer jug body 15', encloses the control unitand forms part of the bottom of the jug. As a lower part of the jug iscut-way, the actual from of the cover is not shown in full. It may beprovided with an aperture to receive an actuator mounted in a base unit,or it may receive a conventional control lever which extends from theside of the jug. In the latter case, the lever would be arranged toco-operate with portion 29 of the control unit.

In order to switch on the jug it is necessary to move portion 29 to theright in order to close a set of contacts within the control unit. Thisalso causes the end of lever 21 to engage with the bi-metal 18. Lever 21is connected by an over center mechanism to the contacts and thearrangement is such that when the steam operated bi-metal 18 reaches asufficient temperature, lever 21 is moved downwardly sufficiently far totrip the over center mechanism and open the contacts within the controlunit 12. The operation of this aspect of the control unit is known inthe art and will therefore not be described further.

FIG. 8 illustrates the inter-relationship between the heating element 1'and the thermal, electrical and mechanical connections of the controlunit 12. The electrical connection is achieved by providing conductingconnection rods 7 in the apertures in the control unit 22 in which thecold tails of a conventional immersion heater are normally received.These are biased upwardly by the spring contacts 23 within the controlunit against the contact portions 6 of the heating element 1'.

Mechanical connection, as discussed above, is made by passing studs orbolts 16 from the heating element 1' through the holes in the controlunit in a manner similar to that employed with traditional elements. Asthe heating element is clamped to the control unit, it compressesresilient seal 17, thereby closing the aperture in the base of the jugin a water-tight manner. The holes through which the bolts are mountedmay be sealed by providing resilient washers under the heads of thebolts.

Thermal connection to the control unit is necessary in order to allowthe over-heat protection systems in the unit to operate. The controlunit is provided with a snap acting bi-metal 24 which, in a conventionaljug, is held in thermal contact with the hot return portion of aconventional element. In the present case it is held directly againstthe bottom of the heating element 1'. In order to ensure a good thermalconnection, it may be necessary to bend the bi-metal upwardly slightlyfrom its usual position, to provide a convex portion on the heatingelement, and/or to apply a small quantity or heat sink compound.

The snap acting bi-metal 24 is connected to a set of electrical contactswithin the control unit and its purpose is to disconnect the supply ofelectrical current from the heating element 1' in the event that theelement overheats, for example as result of having being switched ondry. As a further level of protection, a one-shot cut out device isprovided in the control unit which will permanently disable the controlunit in the event that the previously described over heat protectionsystem out fails to operate. This is in the form of a plastics pin 25which is biased against the bottom of support plate 11 by a springwithin the control unit. The action of clamping the element to thecontrol unit presses the pin against the spring and this holds closed aset of contacts within the control unit. In the event of seriousoverheating, the pin 25 will melt, thereby allowing the contacts toopen. The control unit must then be replaced.

It will be apparent to a person skilled in the art that in thisembodiment of the heater element allows control unit 12 to operate in anentirely conventional manner. Thus the steam control, the overheatprotection system and the one-shot overheat protection device willfunction as if they were connected to the head of a conventionalimmersion heater.

FIG. 9 illustrates a still further version of the heating element. It issubstantially similar to the heating element of the second embodiment,except that it is designed for operation in combination with a controlunit which requires only two mounting bolts or studs. The mounting holes30 are arranged such that a portion of the resilient seal may passaround bolts or studs securing the heating element to a control in use,and thereby preventing leakage of water around the bolts or studs. Thus,no further sealing means such as resilient washers are necessary. Theremaining parts of the element correspond to the second embodiment andreference numerals correspond to those used in respect of thatembodiment.

Whilst the illustrated embodiments have a main track width of 5 mm, thismay of course be varied, depending on the volumetric resistivity andthickness of the conductive track material. For example it has beenfound possible to produce a track having a width of 21/2 mm in its mainpart, and 2 mm and 3 mm respectively in the regions 9a and 9b describedabove. This is advantageous as it allows the plate to be smaller,resulting in a more compact construction, as well as giving a saving inplate material costs.

It is also envisaged that the one shot, further level protection deviceprovided in the known control device (i.e. the meltable pin 25 in FIG.8) may be omitted in view of the back-up protection provided by thepreferentially rupturable regions 9a of the heating element.

I claim:
 1. An electric immersion heater comprising:a support plate; aheating element provided on at least one side of the support plate, theheating element being in the form of a printed circuit conductive track;a control device, the control device having a thermally responsiveactuator; a switch, the thermally responsive actuator cooperating withthe switch to disable the heating element when a temperature of theheating element exceeds a predetermined temperature; and the heatingelement having a localized region to which the control device is clampedby a clamping part, the region further comprising electrical contactportions arranged to make electrical connection to the control devicewhen the control device is clamped to the region, the region being inthermal contact with the thermally responsive actuator.
 2. An electricimmersion heater as claimed in claim 1, wherein the support plate isformed of metal.
 3. An electric immersion heater as claimed in claim 1,wherein the heating element is provided on a bottom side of the supportplate.
 4. An electric immersion heater as claimed in claim 3, whereinthe contact portions have a coating with a lower resistance than otherportions of the region.
 5. An electric immersion heater as claimed inclaim 1, wherein the heating element is substantially flat.
 6. Anelectric immersion heater as claimed in claim 1, wherein the region ofthe heating element is provided with mounting studs or bolts thatconnect the control device to the region.
 7. An electric immersionheater as claimed in claim 6, wherein the region in thermal contact withthe thermally responsive actuator is located between the mounting studsor bolts.
 8. An electric immersion heater as claimed in claim 1, whereinthe width of the track is increased in where the track passes beneath acontrol device seal relative to other portions of the track.
 9. Anelectric immersion heater comprising:a support plate; a heating elementprovided on at least one side of the support plate, the heating elementbeing in the form of a printed circuit conductive track; a controldevice, the control device having a thermally responsive actuator; aswitch, the thermally responsive actuator cooperating with the switch todisable the heating element when a temperature of the heating elementexceeds a predetermined temperature; and the heating element having alocalized region to which the control device is clamped by a clampingpart, the region further comprising electrical contact portions arrangedto make electrical connection to the control device when the controldevice is clamped to the region, the region being in thermal contactwith the thermally responsive actuator, wherein the heating element isprovided with one or more resistance portions that have, as compared toother portions of the heating element, a greater tendency to rupture tothereby disable the heating element.
 10. An electric immersion heater asclaimed in claim 9, wherein the one or more resistance portions areprovided in the region of the heating element within a control deviceseal.
 11. An electric immersion heater comprising:a support plate; aheating element provided on at least one side of the support plate, theheating element being in the form of a printed circuit conductive track;a control device, the control device having a thermally responsiveactuator; a switch, the thermally responsive actuator cooperating withthe switch to disable the heater when a temperature of the heatingelement exceeds a predetermined temperature; and the heating elementhaving a localized region to which the control device is clamped by aclamping part, the region further comprising electrical contact portionsarranged to make electrical connection to the control device when thecontrol device is clamped to the region, the region being in thermalcontact with the thermally responsive actuator, wherein the clampingpart extends at substantially a right angle to a main heating part ofthe heating element.
 12. An electric immersion heater comprising:asupport plate; a heating element provided on at least one side of thesupport plate, the heating element being in the form of a printedcircuit conductive track; a control device, the control device having athermally responsive actuator; a switch, the thermally responsiveactuator cooperating with the switch to disable the heating element whena temperature of the heating element exceeds a predeterminedtemperature; and the heating element having a localized region to whichthe control device is clamped by a clamping part, the region furthercomprising electrical contact portions arranged to make electricalconnection to the control device when the control device is clamped tothe region, the region being in thermal contact with the thermallyresponsive actuator, wherein the support plate is entirely planar andthe clamping part is formed approximately centrally in an underside ofthe support plate with the heating element substantially surrounding theclamping part in a tortuous path.
 13. An electric immersion heater andcontrol unit arrangement comprising:an electric immersion heater, theimmersion heater having a heating element, the heating element being inthe form of a printed circuit conductive track, and a control device,the control device having a thermally responsive actuator, and a switch,the thermally responsive actuator cooperating with the switch to disablethe heating element when a temperature of the heating element exceeds apredetermined temperature, wherein the control device is mounted to theimmersion heater such that the control device is brought into electricalconnection with the heating element, and the thermally sensitiveactuator is brought into thermal contact with part of the heatingelement.
 14. An arrangement as claimed in claim 13, wherein theimmersion heater further includesa support plate, the heating elementbeing provided on at least one side of the support plate, and theheating element having a localized region to which the control device isclamped by a clamping part, the region further comprising electricalcontact portions arranged to make electrical connection to the controldevice when the control device is clamped to the region, the regionbeing in thermal contact with the thermally responsive actuator.
 15. Anarrangement as claimed in claim 13, wherein the immersion heater haselectrical contact portions and the control unit is provided with springcontact members connected to the electrical contact portions of theheating element.
 16. An arrangement as set forth in claim 13, furthercomprising a vessel for receiving water, the vessel including a wall,wherein the immersion heater is provided within the vessel and thecontrol device is mounted externally to the vessel, the part of theheating element being in thermal contact with the thermally responsiveactuator via an opening in the wall of the vessel.
 17. An electric waterheating apparatus as claimed in claim 16, wherein the vessel includes abase, and the control device is located beneath the base of the vesseland the heater is clamped to the control device through the opening. 18.An arrangement as claimed in claim 16, further comprising conductiverods to connect electrical contact portions of the heater and springcontact members of the control device.
 19. An arrangement as claimed inclaim 13, wherein the control device further comprises a one-shotcut-out device.
 20. An electric liquid heating apparatus comprising:aliquid heating vessel having an opening in a base thereof; an electricheater mounted to close the opening, the heater having a liquid heatingsurface disposed inside the vessel, the heater including a support platehaving on its underside an electrically insulating layer on which isprovided a heating element in the form of a printed circuit conductivetrack terminating in electrical contact portions; a thermally sensitivecontrol arranged under and clamped against the underside of the plate,the thermally sensitive control having a thermally sensitive actuator; aswitch, the thermally sensitive actuator cooperating with the switch todisable the heater when the heater reaches a predetermined temperature,the thermally responsive actuator being clamped against and in thermalcontact with a portion of the conductive track; and electrical contactsfor supplying electrical energy to the heating element, the contactsbeing resiliently biased against the contact portions of the heatingelements.